FRESU-WATEIl ALG.E OP THE UNITED STATES. m 



Fig. 3 a, pi. 15, represents part of a sterile filament of this species; 3 h, portion 

 of a pair of fertile filaments, botli magnified 125 diameters. 



Sp. crai^sa, Ktz. 



Sp. Iffite viridis, denique sordide viridis ; articulis sterililjus dianietro sulinequalibns, poi5t divi- 

 sionem interdum fere 5 [ilo broviori))us, autc divi.sionein Siepe fere 2 plo longioribus ; cytin- 

 dermate tenui, bomogeneo, utroque fine nee protenso nee replieato ; fasciis spiralibus 4, 

 deutatis vel tuberculatis, ssepe arctis, subtransversis, tenuibus ; anfractibus li-4 ; ccllulis 

 fructiferis aliis simillimi.s, baud iuflatis ; zygosporis globosis vel cllipticis. 



Diam.—Max. .00G5." 



Syn. — Sp. crassa, Ktz. Rabenhorst, Flora Europ. Algarum, Sect. III. p. 240. 



ffab In stagnis, prope Philadelphia. 



Bright green, but finally a dirty green ; sterile articles about a.s long as broad, sometimes after 

 division only half as long, sometimes before division twice as long; cytioderni thin, homo- 

 geneous, not infolded or produced at the ends ; spiral filaments 4, dentate or tuberculate, 

 often close, subtransverse, thin; turns from 1| to 4 ; fertile cells very like the others, not 

 inflated ; zygospores globose or elliptical. 



Remarks.- — This species is very common in the neighborhood of this city, occur- 

 ring in springs, &c., but especially in the ditches in the Neck. It forms long, 

 lubricous masses, of a bright green color, readily distinguishable by the size of the 

 filaments, which are separated with ease by the unaided eye. I have gathered it 

 repeatedly, in fruit, from the middle of April to the middle of June. In this state 

 the mass has lost its bright green color, and when the filaments are closely examined, 

 even without a glass, minute dark points mark the positions of the spores. 



Fig. 4 «, pi. 15, represents part of a filament commencing reproduction ; 4 &, fila- 

 ments which have matured the spores; 4 c, a pair of conjugating filaments. 



Genus ZYGNEMA. 



Celhilae vegetativte cylindricffi. Massa chloropliyllaeea initio efi"usa et subhomogenea, postea dis- 

 tiuctc granulosa aut per celiuUe lumen distributa, granula amylacea duo ceutralia involvens, aut in 

 eorporibus duobus (in quaque cellula) plus minusve distincte stellatini radiantibus juxta nucleum 

 centralum grauum amylaceum unicum involventibus collocata. Conjugatio scalariformis vel late- 

 ralis. 



Vegetative cells cylindrical. Chlorophyl masses in the beginning effused and subhomogeneons, 

 afterwards distinctly granular, eitlier distributed throughout the cavity of the cell, involving two 

 central starch granules, or gathered togetlier into two masses (in each cell), with more or less dis- 

 tinctly stellate radii and a central starch granule placed near the nucleus, one on each side of it. 



Z. iniiiig^ne, (Hassall) Ktz. 



Z. caespitibns et plerumquo natantibus vel in aqua diffusis, saturate viridibus vel sa>pc sordide 

 flavo-viridibus ; articulis sterilibus diametro circiter a^qnalibus vel duplo longioribus ; conju- 

 gatione scalariforme (et sa;pe simul lateral!, R.); zygosporis globosis; sporodermate Icevi. 



Diani.— Cell „VW = -00126" ; spor. ^^^^%^"—^J-,%^" = 0.00093"— O.OOOIG". 

 Syn. — Tyndaridea insignis, Hassall, Fresh-Water Algoe, vol. i. p. 1 03. 



Zygnema in.wjne, (Hassall) Kutzing. Rabe.niioest, Flora Europ. Algie, Sect. III. 

 p. 249. 

 IJab.— In stagnis, prope Philadelphia ; Wood. Rhode Island ; (S. T. OIney) Thwaites. 



